The fuel tank of a vehicle is normally fixed to the frame or structure of the vehicle such that it maintains a generally horizontal position. During vehicle operation fuel may flow under gravitational or centrifugal action from one side of the tank to the other. Moreover, as the vehicle is operated, pressure builds in the tank.
A significant problem exists when a single fuel induction pipe or conduit is used to draw fuel from the tank. With a single fuel induction pipe or conduit it sometimes happens that, because of fluid flow, the open end of the induction pipe becomes uncovered and the fuel pump will receive air from the induction pipe and deliver same to the engine. Even when two induction pipes are used to draw fuel, there remains the problem that the open end of either pipe may draw air into the system if such open ends are not continually submersed in fluid.
Several devices have been proposed for airplane fuel tanks which encounter similar problems. None of these devices, however, use substantially the entire weight of a gravity actuated means for controlling fluid flow from a fuel tank.